In-flight monitoring of gas turbine engines allows the elaboration of adaptive maintenance plans. By periodically communicating engine data to its service center, the aircraft operator benefits from recommendations from maintenance experts. With additional sensors, maintenance tasks can focus on specific vulnerable parts, rather than reacting to the general behavior of the engine. Design engineers can also anticipate specific problems before they happen, and start working on pre-emptive design modifications. It is well recognized that development work spreads over the useful life of an engine, as some unexpected durability problems, often related to cyclic operation, arise only on aircraft wings.
For the aircraft operator, performance gains are expected from better instrumentation associated with feedback control. Indeed, since engines are currently designed with safety margins, to ensure durability in all conditions, some engines are not operated to the full capabilities of their components. For example, knowing about the severity of the treatment imposed to the most vulnerable turbine parts, it becomes possible to assess the actual thrust capability of a particular engine. Throttle pushes, and hence increases in operating temperatures, can then be applied to healthier engines without sacrificing safety. In addition to pure power gains, reductions in fuel consumption are also possible in the same way, as increasing operating temperatures can improve engine cycle efficiency.
Furthermore, ground tests are expensive, accounting for engine manufacturing, assembly and disassembly costs, and test cell operation costs. Such expenses justify any push toward using as many sensors as possible at one time. In order to validate analytical models, engineers need more than post-testing observations of component deterioration: they need temperature, pressure, and strain real-time measurements, at every running condition of the tests. This detailed lower level information allows to find the root flaws of models. Better monitoring also offers the possibility of shorter tests, avoiding the necessity of reaching high deterioration levels to make useful observations. Experimental parts can therefore be reused for multiple tests.
In instrumenting low access components such as the high pressure turbine of an aircraft engine, lead routing represents a considerable problem, with conventional sensing technology. Each thermocouple, pressure sensor, or strain gauge generally requires a pair of wires to be routed out to the data acquisition system, using a dedicated data transfer slip-ring when installed on a rotating part. This leads to overcrowding of communication lines in low access locations, and requires a large number of data transfer slip-rings when monitoring rotating parts.
The gas turbine engine optimization process requires considerable ground testing and flight experience, and despite all efforts still carries considerable safety margins. In this context, the industry would get considerable benefits from better instrumenting the most vulnerable engine components.